Homeostatis of the prostate gland is dependent on androgens, such that deprivation of the hormone activates a series of poorly-defined molecular events resulting in apoptosis (programmed cell death) of androgen- dependent prostate epithelium and androgen-dependent prostate cancer cells. Integral steps in the process of prostate apoptosis are changes in gene expression and protein phosphorylation initiated by androgen depletion. The androgen receptor (AR) is a nuclear steroid receptor that regulates transcription of androgen-responsive target genes. We have demonstrated that two transcriptional regulatory genes, NGFI-A and c-fos, may be transcriptionally repressed by an AR-mediated mechanism in homeostatic prostate. Transcription of NGFI-A and c-fos rapidly increases prior to apoptosis in the prostate following castration. Additionally, we have established the first in vitro model for prostate cell apoptosis. Using phorbol ester to induce apoptosis in the human prostate cancer line, LNCaP, we have demonstrated a close association between induction of NGFI- A and c-fos and apoptosis of these cells. Pertinent to these findings was the identification of putative androgen receptor binding sites in both genes. Our studies demonstrate specific binding of an AR fusion protein to these binding sites in the NGFI-A and c-fos genes. Moreover, a fragment of NGFI-A containing this site confers transcriptional repression on a luciferase reporter gene when cotransfected with androgen receptor. These studies provide evidence that NGFI-A and c-fos are transcriptionally repressed in homeostatic prostate which are then activated following depletion of androgen. As early response transcription factors, NGFI-A and c-fos may function as regulatory intermediates in prostate apoptosis. It is our hypothesis that AR-mediated regulation of downstream target genes, such as NGFI-A and c-fos, is necessary for apoptotic cell death in prostate. To prove our hypothesis, we will employ in vivo transcription and in vitro and in vivo footprinting assays to identify elements that mediate androgen repression of these genes. To establish the role of NGFI-A, and c-fos in apoptosis of androgen-sensitive prostate cancer cells, we will use our in vitro apoptosis model for antisense and neutralizing antibodies to "knockout" or functionally inhibit NGFI-A and c-fos. In an NGFI-A "knockout" mouse we will examine the effects of NGFI- A loss on castration-induced prostate apoptosis.